The field of the present invention is composites of plastic and wood veneer.
Wood has long been used as both structure and decorative surfacing for furniture and other similar uses and has also been adapted for surfacing nonwood objects such as the interior and exterior components of automobiles. Wood veneer sheeting offers significant virtues such as appearance and strength per unit weight. However, wood is subject to deterioration in many environments. Coatings and laminates have been developed for the preservation of wood. However, these materials tend to be porous, to deteriorate over time, to separate from the wood and/or to require frequent attention. These characteristics have proven to be dissatisfactory in a significant number of applications where longevity and maintenance of appearance without repeated treatment are necessary.
Wood is made up of cells. Each cell consists of an outer cell wall defining a cell cavity. Cells contain sap, moisture and even air. The cell walls contain an amorphous polymeric substance, lignin, which, together with cellulose, forms the fiberous cell walls. Lignin also is the binding material between cells. The cells take in and give off moisture depending on the temperature and humidity of the environment. These changes can cause movement within the grain structure which may in turn lead to splitting, cracking, curling, buckling and warpage.
For aesthetic uses, wood is frequently used as a veneer over structural wood or other materials. Veneer is usually sliced to a commercial thickness of between 0.010 inches and 0.060 inches. Even in such thin sheets, it still contains multiple layers of cellulose cell structures bonded together and interspersed with lignin. The thin nature of wood veneers makes them even more susceptible to the effects of the environment if not properly applied, sealed and maintained. It is these cells which act as sponges to retain and release moisture relative to atmospheric and environmental conditions.
To overcome the effects of the environment, coatings have been employed which are intended to seal a wood surface and, in some instances, are partially dispersed into the wood. The coatings typically do not disturb the cells which remain in tact and responsive to environmental change. Coatings are typically unable to provide a complete barrier to moisture as they are seldom wholly impervious to moisture. Joints and cracks also provide opportunities for moisture intrusion. Standard commercial coatings which retain the appearance of the grain include varnish, polyurethane and many other types of liquid coatings. These have limited utility and are best in protected environments. Plastics have also been used to totally encase wood. Such uses have had difficulties in application, retained integrity, cost and/or inconvenient coating thickness.
Laminations are also employed. Laminations employ sheet material bonded to wood surfaces. They are very much limited in their ability to preserve the structure and appearance of wood. The bonding of laminates typically does not influence the adjacent cell structure; and leakage at a joint or a crack can result in deterioration of the wood and delamination.